Photographic silver halide emulsions which include high efficiency sulfurcontaining sensitizers



United States Patent 3,501,313 PHOTOGRAPHIC SILVER HALIDE EMULSIONS WHICH INCLUDE HIGH EFFICIENCY SULFUR- CONTAINING SENSITIZERS Jozef Frans Willems, Wilrijk-Antwerp, Paul Faelens, Schilde, Frans Henri Claes, Edegem, Hendrik Alfons Borginon, Mortsel-Antwerp, and Walter Camiel Pattijn, Hemiksem, Belgium, assignors to Gevaert-Agfa N.V., Mortsel, Belgium, a Belgian company No Drawing. Filed Oct. 11, 1966, Ser. No. 585,732 Claims priority, application Great Britain, Oct. 11, 1965, 42,974/65 Int. Cl. G03c 1/28 U.S. Cl. 96107 12 Claims ABSTRACT OF THE DISCLOSURE Photographic light-sensitive emulsions are disclosed which include a sensitizer having the formula wherein:

A is a sulphur atom,

each of R R R and R is hydrogen, alkyl, or aryl, or

R and R and/ or R and R together are the atoms necessary to close a heterocyclic ring, and

n is zero or one.

The present invention relates to chemically sensitized, photographic, light-sensitive silver halide emulsions and to a photographic material comprising a light-sensitive layer coated from such emulsion.

It is known that photographic silver halide emulsions can be chemically sensitized by means of dilierent kinds of compounds, which considerably enhance the sensitivity and sometimes the gradation too. The known chemical sensitizers can be divided into three main classes:

(a) Compounds comprising a labile sulphur atom, the so-called sulphur sensitizers, among which sodium thiosulphate and the thiourea compounds are best known;

(b) Reducing compounds such as tin (II) chloride and thiourea dioxide;

(c) Salts of noble metals such as gold, platinum or palladium salts.

It is also known that the light-sensitivity of silver halide emulsions, at least to some extent, results from the presence of sulphur compounds in the so-called active gelatin.

Since the use of inert gelatin for the preparation of silver halide emulsions finds more and more acceptance in the photographic industry, the use of chemical sulphur sensitizers has become of increasing interest. The known sulphur sensitizers such as sodium thiosulphate and thiourea compound however are only usable in specific experimental conditions. They act only in rather narrow pH-ranges and at specific pAg-values of the emulsion. For instance, sodium thiosulphate can be used as chemical sensitizer for washed silver bromide emulsions but only a slight increase in sensitivity is observed in the case of silver chloride emulsions and no increase at all in the case of silver iodide emulsions. Unwashed silver bromide emulsions too, i.e., emulsions with high pAg-value, can only be very dilficultly sensitized with the known chemical sulphur sensitizers.

3,501,313 Patented Mar. 17, 1970 It has now been found that compounds corresponding to the following general formula:

A represents a single bond or a sulphur atom, and

each of R R R and R represents a hydrogen atom, an alkyl radical including a substituted alkyl radical, an aralkyl radical, and a substituted aralkyl radical, or an aryl radical including a substituted aryl radical or R and R and/ or R and R together represent the atoms necessary to close a heterocyclic ring including a substituted heterocyclic ring,

are very interesting chemical sulphur sensitizers for lightsensitive photographic silver halide emulsions no matter whether they are silver chloride emulsions, silver bromide emulsions, silver iodide emulsions, emulsions of a combined silver halide type, washed emulsions or unwashed emulsions. Moreover, the compounds according to the above general formula produce all kinds of other favourable side-efiects on the silver halide emulsion. For instance, they contribute in a considerable way to the homogeneity of the grain size in that they prevent the exceptional growth of some grains when present during the physical ripening of the silver halide emulsion. In consequence thereof, the compounds according to the general formula are very interesting when employed in the preparation of fine-grain silver halide emulsions, for instance emulsions the silver halide grains of which have an average diameter of less than 0.2 micron. In such fine-grain emulsions the compounds according to the general formula are also particularly suitable as chemical sensitizers when used as a partial or full substitution for the usual sodium thiosulphate which, owing to the large specific grain surface of such fine-grain emulsions, would have to be added in large amounts. This would result in an undesirable growth of the silver halide grains since said large amount of thiosulphate would create a strong dissolving action.

Examples of appropriate chemical sulphur sensitizers according to the above general formula are:

(5) N, N-dibenzyl dithio-oxamide i) N, N-bis(m-sulphobenzyl)-dithio-oxamide, diammonium salt N-p-sulphophenyl-dithio-oxamide, sodium salt mop-@rrn-p-gasm i) N, N-diphenyl-dithio-oxamide .0) B is- (dimethyl-thioearb amoyl) sulphide H 8 CH N- C S C N H3 g g CH3 .1) Bis (pip eridino-thiocarb onyl) -sulphide CHr-CHZ CHz-CHZ HzC NC SCN CH2 cHrcfiz g g CH2Cfi2 The optimum amounts to be applied of sulphur sensiizers according to the above general formula depend upon he compound chosen, the nature of the silver halide, he grain size, the desired ripening time, the ripening emperature, the pH and pAg of the silver halide emulion. However, the amounts used generally vary from bout 1 mg. to about 200 mg. per mole of silver halide. t is evident that smaller amounts of these compounds say be used too, e.g., when a little increase in sensitivity envisaged. When using larger amounts care should be zken that no fog arises.

The new compounds may be used in combination with educing sensitizers such as tin (II) salts or thiourea di- -xide. Very interesting additive increases in sensitivity re obtained when the new sensitizers are applied in comination with gold salts, such as gold thiocyanate, platiurn salts and palladium salts. A considerable increase in ensitivity can also be obtained when applying the comounds according to the present invention in combination rith development accelerators such as polyoxyalkylene erivatives having a molecular weight higher than 500 nd onium compounds.

The new sulphur sensitizers can be used in spectrally s well as in not spectrally sensitized emulsions. They are ucecssfully applied in common emulsions, in colour mulsions, in X-ray emulsions, in graphic emulsions, in .ippman emulsions and in fine grain emulsions for scienific purposes.

The classical emulsion ingredients such as stabilizers, ntifogging agents, developing agents, hardening agents, olour couplers, softening agents, dispersing agents, etc., my be incorporated into the emulsion together with the ulphur sensitizers according to the invention without any etrimental interaction taking place.

Although the use of the sulphur sensitizers according a the above general formula is of great technological nportance to sensitize silver halide emulsions prepared Ilth inert gelatin, it is also very interesting to use them or the sensitization of silver halide emulsions the proactive colloid of which at least partially consists of active elatin or other hydrophilic colloids such as polyvinyl lcohol.

When necessary, the compounds may also be used in ombination with known sulphur sensitizers in order to btain special effects such as very high maximum denities and high gradations together with high sensitivities.

The following examples illustrate the present invention.

EXAMPLE 1 A silver bromo-iodide emulsion (3 mole percent of iodide) prepared with inert gelatin and having an average grain size of 0.5 micron, a pAg of 7.5 and a pH of 6.5 is divided into three equal parts (samples A, B and C). The sulphur sensitizers listed in Table I are added to samples B and C in the given concentrations. The emulsions are then ripened at 45 C. for 3 hours whereupon they are coated on a cellulose triacetate support. The test-strips obtained are developed after exposure in a hydroquinone-p-rnonomethyl-aminophenol hemisulphate developer, fixed and rinsed whereupon the speed is meas ured. In Table I the relative speeds are listed.

A gold thiocyanate solution is added in an amount equivalent to 5 mg. of gold per mole of silver halide to a same emulsion as described in Example 1 just before dividing the emulsion in samples A, B and C and before the addition of compounds 2 and 3 in the given concentration to samples B and C. The three samples are coated and further treated as described in Example 1. The materials according to the present invention show a sensitivity that is 3 times as high as that of the light-sensitive material containing only gold rhodanide and no chemical sensitizer according to the present invention.

EXAMPLE 3 An all-silver iodide emulsion prepared with inert gelatin and having a pAg of 9 and a pH of 6 .5 is divided into four equal parts A, B, C and D. To each part is added the chemical sensitizer listed in Table II hereinafter in the concentration given. After having been ripened for 1 hour at 50 C. the four emulsions are coated on a cellulose triacetate support. The light-sensitive materials obtained are exposed and further treated as described in Example 1. The relative speeds are given in Table II.

TAB LE II Concentration per Sulphur sensitizer mole of silver halide Rel. speed B Sodium thlosulphata. 1.10- mole 100 C Compound 1 1.10- mole 200 Compound 5 1.10- mole.

EXAMPLE 4 TAB LE III Concentration per Sulphur sensitizer mole of silver halide Rel. speed 100 Sodium thiosulphate 0.7X10- mol 200 C Compound 10 0.7)(10- mole 350 EXAMPLE 5 To the same kind of emulsion as described in Example 4 a gold thiocyanate solution is added, in an amount equivalent to 7 mg. of gold per mole of silver halide, before dividing the emulsion into samples, and adding a chemical sensitizer according to the invention. The emulsion is divided into two equal parts and to one part 0.7 mole of compound 10 per mole of silver chloride is added. The emulsions are coated and further treated as described in Example 4. The speed of the lightsensitive material comprising compound 10 is 3 times as high as that of the other material.

EXAMPLE 6 An ammoniacal silver bromo iodide emulsion (3 mole percent of iodide) which has been prepared with inert gelatin, and which has not been washed as was the case with the emulsions of the preceding examples, is divided immediately after its preparation into 3 equal parts (samples A, B and C). The sulphur sensitizers listed in Table IV are added to samples B and C in the given concentrations. After having been kept for 30 min. at 35 C. the three samples are coated onto a cellulose triacetate support and further treated as in Example 1. The relative speeds of the three materials are listed in Table IV.

240 cc. of a 3M aqueous silver nitrate solution and 240 cc. of a 3M aqueous potassium bromide solution are simultaneously and slowly added at 35 C. to a solution of 50 g. of gelatin in 500 cc. of water (emulsion A). A second emulsion is prepared in the same way with the only difference that the aqueous gelatin solution to which the aqueous silver nitrate and the potassium bromide solutions are added also comprises 9 mg. of compound 2 (emulsion B).

Emulsions A and -B are physically ripened by keeping them for 60 min. at 45 C.

Electron micrographs (magnification 10.000 X) are taken from the ripened liquid emulsions. In both cases, these micrographs shows a dispersion of silver bromide grains ranging for the greater part from about 0.05 to about 0.11.0. Emulsion A, however, also contains a considerable number of grains ranging from about 0.5 to about 1.0 1. whereas emulsion B only contains some grains which are of larger size than 0.1,u. From the results obtained it clearly appears that the presence of a chemical sensitizer according to the present invention during the precipitation of the silver halide and the physical ripening of the emulsion obtained prevents in a very efiicient way the formation of large silver halide grains.

We claim:

1. Photographic light-sensitive silver halide emulsion containing as a sensitizer at least one compound corresponding to the following general formula:

wherein:

A is a sulphur atom,

each of R R R and R is hydrogen, alkyl, or aryl, or

R and R and/or R and R together are the atoms necessary to close a heterocyclic ring, and

n is zero or one.

2. Photographic light-sensitive emulsion according to claim 1, wherein the silver halide emulsion includes a protective colloid consisting substantially of inert gelatin.

3. Photographic light-sensitive emulsion according to claim 1, wherein the emulsion is an unwashed silver halide emulsion.

4. Photographic light-sensitive emulsion according to claim 1, wherein the silver halide of the emulsion consists substantially of silver chloride.

5. Photographic light-sensitive emulsion according to claim 1, wherein the silver halide of the emulsion consists substantially of silver iodide.

6. Photographic material comprising a light-sensitive silver halide emulsion layer applied from the silver halide emulsion of claim 1.

7. The photographic light-sensitive emulsion of claim 1 wherein the emulsion is a fine grain emulsion.

8. Photographic light-sensitive emulsion according to claim 1, wherein the emulsion includes a polyoxyalkylene derivative having a molecular weight higher than 500.

9. Photographic light-sensitive emulsion according to claim 1, wherein the emulsion includes an onium compound.

10. Photographic light-sensitive emulsion according to claim 1, wherein the sensitizer is present in an amount of from 1 to 200 mg. per mole of silver halide.

11. Photographic light-sensitive emulsion according to claim 1, wherein the emulsion includes a gold salt.

12. Photographic light-sensitive emulsion according to claim 11, wherein said gold salt is gold thiocyanate.

References Cited UNITED STATES PATENTS 3,226,232 12/1965 Dersch et a1 96-107 X 3,287,137 11/1966 McBride 96-107 NORMAN G. TORCHIN, Primary Examiner A. T. SUROPICO, Assistant Examiner US. Cl. X.R. 96-108 

